Acting on mounting evidence linking clinical depression to cardiovascular disease, researchers sought to explore whether other forms of depression might also increase the risk for conditions affecting the heart or brain.

They examined a registry of 1.8 million California women who did not have a history of cardiovascular disease or chronic depression. Of those women, 40,276 were diagnosed with postpartum depression.

Within roughly five years of giving birth, the women who had postpartum depression had a nearly 70 percent higher risk of developing cardiovascular disease, including heart attack, stroke and heart failure. And that was even after adjusting for traditional cardiovascular risk factors such as diabetes and high blood pressure, pregnancy-related conditions such as preeclampsia, and social and behavioral factors such as smoking, alcohol use and insurance access.

The findings will be presented Nov. 11 at the American Heart Association's Scientific Sessions meeting in Chicago.

What's causing these women to be more at risk is uncertain, said Dr. Punag Divanji, the study's lead researcher and a cardiologist at the University of California, San Francisco.

Among the possibilities is a link to the drop in estrogen and progesterone after childbirth. These two hormones increase exponentially during pregnancy, and women with postpartum depression may have a greater decline in levels after childbirth than other new mothers.

But more research needs to be conducted before actual causal reasons can be pinned down, Divanji said.

"There's still a lot of work to be done in terms of better understanding cardiovascular risk in women," he said, particularly risk factors other than high blood pressure, high cholesterol and diabetes.

Dr. Leslie Cho, director of the Women's Cardiology Center at The Cleveland Clinic, agreed that more research would help validate the findings, as well as shed light on the mechanics behind them.

"What we do know is that if you're depressed, straight-up depressed, you tend to eat badly. You tend to drink. If you're depressed, you don't tend to exercise," said Cho, was not connected with the new study. "It goes with so many other unhealthy lifestyle choices."

Past studies have shown a link between clinical depression and its impact on cardiovascular disease, including high blood pressure, Cho said.

"It's been linked with platelet reactivity -- your platelets are more sticky when you're depressed," meaning there's a greater chance they could clump and form a blot clot, she said. "So, there are all sorts of interesting heart-brain connections there."

She noted that women of all ages should consider having their cardiovascular risk assessed anyway because heart disease is the leading cause of death for women.

Divanji said he hopes the study will help raise awareness about the potential link between all types of depression and cardiovascular disease.

"This level of evidence isn't sufficient enough to say we need to sound the alarm but rather, this is something to be aware of and think more about," he said. "When we see patients, we should be cognizant that depression plays a role in future cardiovascular disease risk."